1. Field of the Invention
The invention relates generally to data communication and, in particular, to acoustic conveyance of information across an air gap between devices.
2. Description of the Related Art
During the latter half of the 20th century and prior to telecom deregulation, it was generally illegal to make an electrical connection to the public telephone network. At the same time, most premises telephones were hard-wired to wall terminals. Modular connectors like RJ11 had yet to be standardized. Nonetheless, with increased use and popularity of computing, techniques were needed to facilitate data interchange.
In part due to the ubiquity and physical uniformity of telephone handsets in businesses and homes, acoustic couplers were developed to connect modems to the telephone network. Speeds were typically 300 bits per second, achieved by modulating a carrier at 300 baud. One such device was the acoustic data coupler 300 modem introduced in 1968. Some of the basic technologies employed in such devices are described in U.S. Pat. No. 3,553,374. Acoustic modems became popular for encoding digital information using audible signals acoustically coupled into the phone network and transmitted as voice-band, analog signals over phone lines. Today, acoustically coupled devices have all but disappeared, except perhaps from museum collections. Even the once familiar, legacy-based tones and grinds of “dial up” negotiation have begun to disappear from our experience, replaced by Ethernet connections to cable/ADSL/satellite services, or 802.11x wireless (also called WiFi) connections. In each of the modern high-bandwidth communications services, acoustic transducers and even voice-band electronically-coupled startup negotiation sequences have long since been abandoned.
Modern modulation/demodulation devices (whether or not denominated as modems) are essentially silent, typically utilizing radio-frequency (RF) or higher-frequency electromagnetic energy conveyed over wires, in optical cables or waveguides and/or through freespace. Given the capabilities of these newer technologies and the very much higher bandwidth demands typical of modern data communications, mobile telephony and multimedia, etc., some might say that the era of acoustic modems has reached its end.